1. Field of the Invention
The invention is generally related to medical devices used for lowering intra-abdominal pressure (IAP) in patients.
2. Description of the Prior Art
Abdominal decompression has been investigated for a number of years in connection with the treatment of pregnant women. Specifically, studies have been conducted to evaluate the ability of abdominal decompression to ease the pain of labor, to increase intra-uterine fetal growth, or treat toxemia of pregnancy. In all previous investigations, abdominal decompression was performed intermittently at high negative pressures for short periods of time (e.g., -70 mm Hg for 30 seconds every minute for 30 minutes, twice daily).
Heyns, Obstet. Gynaecol. Br. Commonw., 66:220-228, 1959, discloses a study wherein intermittent abdominal decompression is used for the treatment of labor pains during the first stage of labor. Eight patients were used in the study, and the patients controlled the negative pressure themselves by placing a finger over a vent tube to bring the pressure down to around 50 mm Hg in most instances for about sixty seconds. However, in some cases the pressure was brought down to as low as 150 mm Hg. The article reports that the labor pains were relieved in all eight patients, and that the treatment did not interfere with diagnosing the second stage of labor (actual commencement of delivery).
Heyns et al., Lancet, 1:289-292 (1962), present data from a study using intermittent abdominal decompression for thirty minutes on twelve or more occasions in 350 caucasion women during the last two months of pregnancy and during labor. In the study, amniotic fluid pressure was measured and it was found that this pressure rose to 40 mm Hg during early labor, and 50-70 mm Hg during mid-labor as the second stage approached. It was found that abdominal decompression lowered these pressures to zero or less at the height of a uterine contraction. The highest pressures were found in the small primigravida with a tight belly wall and in active athletes. The fetal heartbeat did not change in rate during uterine contractions with decompression. The placenta from women treated with decompression was reported to have a richer arteriolar and capillary network. In a non-randomized study, the perinatal death rate in babies subjected to decompression was 0.6%, compared to 3% to a non-treated group. The authors concluded that the data suggests that decompression improves fetal oxygenation.
There have been two other studies using intermittent abdominal decompression for the first stage of labor by Quin, L J et al, which are found in Amer. J. Obstet. Gynecol. 83:458, 1962, and J. Obstet. Gynaecol. 71:934, 1964. The device was used in 100 primiparas and 42 multiparas in the first study and 302 primiparas and 188 multiparas in the second study, and there was an 86% excellent or good pain relief response with its use. The device was modified with a switch to the vacuum pump which the patient activated at the onset of labor pain and turned off at the completion of a contraction. This device was manufactured by the J. H. Emerson Co., Cambridge, Mass., and called the "Birtheez".
Blecher et al., Lancet, 2:621-625, 1967, reports on a study with fifty caucasion and 80 non-white patients treated by abdominal decompression applied for ten minutes twice on the first day of treatment, twenty minutes twice on the second day of treatment, and thirty minutes twice on the third and subsequent days of treatment. Toxemia of pregnancy was hypothesized to be secondary to uterine ischemia produced by increased IAP, and that abdominal decompression would prevent this ischemia and prevent or correct toxemia. The pressures used in the study were individually gauged according to the patients' tolerance, and were generally between -50 and -80 mm Hg for 15 seconds in every 1/2 minute. It was reported that the treated patients whose hypertension was secondary to toxemia had a significantly better response, and that they had a significantly better fetal survival rate.
Coxon et al., J. Obstet. Gynaecol. Br. Commonw., 78:49-54, 1971, reports on a study wherein the authors used the radioisotope indium 113 m bound to transferrin and an external counter and observed a 30% increase in placental count rate with abdominal decompression. The use of abdominal decompression during a uterine contraction in the first stage of labor resulted in a 15% increase in placental site count rate over the uterine wall away from the placental site. The authors apparently used test conditions where approximately -70 mm Hg abdominal decompression was applied, but the frequency and duration were not provided. The Coxon et al. study appears to support the Heyns hypothesis that abdominal decompression improves fetal blood flow.
Macrae et al., J. Obstet. Gynaecol. Pr. Commonw., 78:636-641. 1971, reports on a study where intermittent abdominal decompression (negative pressure of -70 mm Hg applied for fifteen seconds of every minute over a 1/2 hour period, with treatment sessions ranging from 2-3 times per week) was asserted to raise estriol levels to normal. Dysmaturity, which is associated with a high perinatal mortality, is associated with decreased estriol levels.
Varma et al., J. Obstet. Gynaedol Br. Commonw., 80:1086-1094, 1973, studied intermittent abdominal decompression in 70 pregnant patients with "small-for-dates" fetuses as compared to 70 similar control cases. The decompression group received abdominal decompression once a day in the Heyns decompression suit in which they were placed for thirty minutes using a negative pressure of 80-90 mm Hg for 25 seconds every minute. Ultrasound cephalometry and 24-Hr urinary estrogen levels were measured. The mean fetal growth rate of the decompression group was significantly greater than the untreated group and was associated with a significantly higher estrogen excretion and lower incidence of fetal distress as well as a significantly higher Apgar score and a lower percent of low birth weight babies and perinatal mortality.
Hofmeyr, "Abdominal decompression during pregnancy", in Effective Care in Pregnancy and Childbirth, Chalmers I, Enkin M, Keirse M J N C, eds., Oxford University Press, Oxford, 1989, pp. 647-652, provides a review of the literature on abdominal decompression and describes the apparatus, the technique, and indications for its use. However, it is concluded that: "There is some evidence that abdominal decompression may be of value in certain abnormal states of pregnancy but the studies reported to date are not of sufficient methodological quality to support the use of abdominal decompression except within the context of further methodologically sound, controlled trials. Nevertheless, there are so few options for managing the compromised fetus other than elective delivery that it is important to subject abdominal decompression to further evaluation."Hoffmeyr et al., Br. J. Obstet Gynaecol., 97:547-548, 1990, provided a further evaluation of a previous randomized controlled trial designed to test the hypothesis that higher developmental quotients would develop in infants born to mothers treated with intermittent abdominal decompression secondary to improved fetal blood flow. The patients were randomized to treatment or control groups, and the treated group received abdominal decompression three times per week from thirty weeks of gestation using patient controlled decompression for fifteen seconds each minute over thirty minutes. No differences in gestation time, birthweight at delivery or one minute Apgar scores were noted between the groups.
In an editorial, Hofmeyr, Br. J. Obstet. Gynaecol., 97:467-469, 1990, suggests that the negative reaction to the failure of abdominal decompression to improve fetal development scores or intelligence quotients in normal pregnancies, as initially suggested by Heyns, may detract from its possible benefits to decrease the pain of labor and fetal distress, or treat toxemia or poor fetal growth which may be secondary to impaired placental blood flow.
Shimonovitz et al., Br. J. Obstet. Gynaecol., 99:693-695, 1992, describe three women with a "bad obstetric history", e.g., multiple recurrences of toxemia, severe intrauterine growth retardation, and fetal death, who were treated with intermittent abdominal decompression (-70 mm Hg for thirty seconds every minute for thirty minutes, two times a day) with excellent results including correction of hypertension and improved fetal growth.